Advantages and disadvantages of sulfuric acid cleaning and sodium hypochlorite cleaning
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Sulfuric acid cleaning, sodium hypochlorite cleaning. Small footprint (one cleaning tower and several heat exchangers); (two cleaning towers, no heat exchangers required). Operation method: (Simpler setup process, adjustment via metering pump); (Involves a setup process, relatively more dangerous). Post-treatment: (Small amount of waste sulfuric acid, but few recycling options); (Large amount of sodium hypochlorite used, difficult wastewater treatment, emissions do not meet standards). Maintenance: (Incomplete elimination of sulfuric acid emissions, danger during maintenance); (Simple maintenance method, replacement with water sufficient). Economic comparison: To produce 1000 T of PVC, 25 T of sulfuric acid and 2500 m³ of sodium hypochlorite are required, with 160 m³ of production water needed for replenishment. Therefore, the cost of auxiliary materials used for sulfuric acid cleaning is 35,000 yuan (with the unit price of sulfuric acid being 1,400 yuan). The cost for sodium hypochlorite cleaning is 11,000 yuan, which includes the costs associated with water, alkali, chlorine, and the treatment of waste sodium hypochlorite. Labor costs are lower for sulfuric acid cleaning, as there is no need to deal with waste sodium hypochlorite, saving 660 yuan. In terms of energy consumption, sulfuric acid cleaning requires 150 kW/h of power, resulting in costs of 1,080 yuan; sodium hypochlorite cleaning requires 310 + 150 kW/h, resulting in costs of 3,312 yuan. Sulfuric acid cleaning requires 270 m²/h more heat exchange area compared to sodium hypochlorite cleaning, and the cost associated with heat exchange is 620 yuan (calculated based on our unit’s cost structure and the heat exchange area required by the 7°C water cooler used in acetylene cleaning). Excluding maintenance and labor costs, the cost of producing 1,000 tons of PVC using sulfuric acid cleaning is 35,000 + 1,080 + 620 = 36,700 yuan. The cost of producing 1,000 tons of PVC using sodium hypochlorite cleaning is 11,000 + 3,312 + 660 = 14,912 yuan. The figures above are based on personal calculations; please feel free to point out any inaccuracies or errors. Follow-up questions: 1. Is the cleaning effect of sulfuric acid better than that of sodium hypochlorite? 2. Can waste sulfuric acid be added to the supernatant, and can cement plants accept it?
After treatment with spent sodium, all water is reused; only a portion containing sludge is discharged to the wastewater treatment facility
The advantage of using sulfuric acid for cleaning is that it is safe and effective. The main issue is that waste sulfuric acid is difficult to handle due to its color; previously, fertilizer factories used it. If it were possible to address the color problem of this waste sulfuric acid, there would likely be a good market for it
The original poster has analyzed this very carefully, but there are a few points to clarify: the specific consumption of sulfuric acid should be below 20 kg/tPVC; since your value is 25 kg/t, you need to investigate the process factors at play； The price of sulfuric acid is not 1400 anymore; it’s around 300 at present. Almost no one wants waste sulfuric acid, so people either add it to calcium carbide slag or turn to Shanghai Jiawen for waste sulfuric acid recycling services ； Sodium hypochlorite cleaning can cause some damage to the cement produced; calcium carbide slag contains chloride ions, which affect the quality of the cement. Sodium hypochlorite-based dry acetylene generation also consumes some acetylene gas, resulting in high calcium carbide consumption.
The consumption of sulfuric acid is below 20 kg per ton of PVC, and its price is around 300; this can indeed help save some costs. The information I have comes from various sources. My company does not use sulfuric acid for purification purposes; it’s just an idea that came to mind, as there are issues with dealing with defective sodium hydroxide, and at the same time, there’s no proper way to dispose of waste sulfuric acid. It’s not clear whether adding it to calcium carbide slag or the supernatant fluid would be appropriate. If waste sulfuric acid is recycled, then it loses its meaning. Sodium hypochlorite-based dry acetylene generation also consumes some acetylene gas, resulting in high calcium carbide consumption. What is the reason for this?
The generation temperature of acetylene in the dry method is higher than that in the wet method; some hyposodium reacts with acetylene
Is there any connection? Cleaning is carried out after cooling and compression; the outlet temperature of the compressor in our facility is around 30°C, so it shouldn’t have any impact
Sodium hypochlorite can be ignored under low-temperature conditions; it undergoes partial reaction inside the generator
We don’t use waste sodium hydroxide water internally
Oh, then how do you deal with that defective sodium?
We have a process for treating defective sodium hydroxide; after treatment, the sodium hydroxide is recombined. 5 to 6 cubic meters of production water are added per hour, and the same amount of wastewater is discharged. The chloride content in the sodium hydroxide is high, and cement plants do not want it once it is added